Prior vagotomy blocks VMH obesity in pair-fed rats

Previously vagotomized, ventromedial hypothalamus (VMH)-lesioned rats and sham-lesioned controls were maintained on an intragastric pair-feeding regimen in which nonvagotomized VMH rats deposit excessive fat. Hypothalamic lesions were produced after 6 days of adaptation to pair feeding, and the experiment continued for 30 days postlesion. Extent of vagotomy was determined with a multiple-regression procedure with cell loss in the dorsal motor nucleus of the vagus, fasting gastric contents, and basal pancreatic protein output as predictor variables. The correlation was 0.95 between this set of indexes and the adequacy of a vagotomy for preventing hypothalamic obesity. Thus, radical vagotomies precluded the typical accumulation of significantly increased levels of carcass fat in lesioned animals (16.3 vs. 14.0% for controls). VMH rats with less extensive transections accumulated substantially more fat (25.9%). This outcome suggests that vagotomy produces a specific blockade of lesion-produced disturbances in metabolism leading to obesity. It fails to support a previous suggestion that vagal section blocks VMH obesity merely as a nonspecific surgical restriction of food intake because vagotomy was effective even though its effects on food intake could not operate.